Artificial hearts are known and widely used, for example, in heart-lung machines. U.S. Pat. No. 3,097,366 describes and shows a heart pump in which the ventricle-simulating chambers of the pump are worked upon by a common motor driving a plate which causes the chambers to deflate and inflate alternately. The chambers have the form of rubber bags and receive blood from atrium chambers arranged to function as pressure equalizers, i.e., to produce a uniform inflow of blood. The two pumps act on the outflowing blood as "positive" pumps in which the displacement volumes, or stroke volumes, do not vary, and only the rhythm (frequency) can be regulated.
U.S. Pat. No. 3,783,453 describes and shows a double pump in which the ventricle chambers, which have the form of rubber bags, are each enclosed in a respective rigid container and are acted upon externally by a working fluid that is injected into and drawn out of the container. The pump bags are caused to pump alternately, and the function is regulated by a control system in a manner such that the same amount of blood per unit of time, when seen overall, is pumped through the two pumps. This control is effected by separate sensing of the bag volumes.
The present invention is the result of a discovery by the inventor that the human heart does not work in the manner normally presumed. Since this discovery constitutes the background to the invention, it is described briefly below in order to enable the invention to be more readily understood. A more detailed description of the inventor's findings is found in Lundback, S. "Cardiac Pumping and Function of the Ventricular Septum." Supplementum 550 1986 to Acta Physiologica Scandinavica (ISBN 91-7900-066-5).
It was observed from, inter alia, ultrasonic investigations of the anatomical heart, that during one heart beat the volume of the heart often changes by less than about 10% of its total volume, and that the incoming blood does not pulsate to any great extent while the outgoing blood pulsates strongly. From this it was possible to predict, and to establish clinically, that when the heart beats, the heart musculature, upon contraction of the heart muscles, draws the atrium septum, including the heart valves, down towards the tip of the heart. When the heart muscles then relax, the valve plane is pressed upwards, not by the force exerted by the muscles, but by the intrinsic diastolic pressure of the blood supplied and the force exerted by elastic components within and externally of the heart. Thus, during the systole phase the volume of the ventricle decreases, while that of the atrium increases, wherewith the sum of these volumes decreases slightly and the outer form of the heart thus decreases. Consequently, during the systole period, more blood is pumped out than comes in. The inflow of blood to the atrium continues, however, during the systole period, due to the fact that the atrium volumes increase. During the diastole phase, the valves in the aorta and the pulmonary artery are closed. The inflow of blood to the atrium continues, because the total volume of the heart increases slightly and the valve plane again moves upwards, more or less in response to the amount of blood entering the atrium, whereby the volume of the heart beat in the next following systole phase is determined by the amount of blood supplied during the preceding diastole and systole periods. These discoveries, together with a further discovery pertaining to the regulating function of ventricle septum, must be considered surprising and are thought likely to result in paradigmatic changes in this particular science.
It has also been observed, according to these new discoveries, that the human heart has a particular, natural method of regulating the quantities of blood pumped in the two halves of the heart in a manner to achieve the necessary balance. The regulation is due to the flexibility of the ventricle septum. During the systole phase, in which the volumes of respective heart chambers are compressed, there is experienced on the outlet from the right ventricle to the pulmonary artery a lower counter-pressure, since the resistance to flow in the pulmonary section of the circulatory system is lower than the resistance to flow in the systemic section of the blood circulatory system, which passes through the aorta. The ventricle septum will therefore always take a given position in which it is deflected systolically towards the right chamber. On the other hand, during the diastole phase the ventricle septum is able to adopt a variable position, in dependence upon the pressures prevailing at the two inlets, resulting in a balancing function of the quantities of blood pumped. This balancing function of the heart is of particular importance, and it has been observed, for example, that an infarct concerning the ventricle septum has a worse prognosis than an infarct concerning other parts of the right and left ventricles of the heart. This would seem to be due to the fact that the ventricle septum loses its stablizing function during the systole phase, and becomes rigid and immovable. In consequence, the amount of blood pumped from the right ventricle chamber increases while, at the same time, the output from the left ventricle chamber decreases to the same extent, causing blood to collect in the lungs, resulting in pulmonary edema.